Method of manufacturing a protein gel

ABSTRACT

A method of manufacturing a protein gel. In the first step, a protein-containing solution is heated for sterilization. In the second step, the protein-containing solution is cooled, and an enzyme is added to the protein-containing solution. In the subsequent third step, the protein-containing solution and the enzyme are mixed while maintaining the temperature in the second step so as to obtain a mixture. In the fourth step, the mixture is aseptically filled in a food container. In the fifth step, the aseptically filled mixture is allowed to stand at ambient temperature, during which the enzyme denatures the protein in the protein-containing solution. Since the mixture is not required to be heated for denaturing the protein in the protein-containing solution, the energy consumed in the manufacturing process is reduced, thereby lowering the manufacturing costs.

This is a National Stage Filing of PCT/JP95/00236, filed Feb. 20, 1995.

TECHNICAL FIELD

The present invention relates to a method of manufacturing a proteingel.

BACKGROUND ART

In conventional methods of manufacturing a protein gel such as tofu(bean curd) in which an aqueous solution containing protein (hereinafterreferred to as "protein-containing solution") is filled in a foodcontainer for curdling therein, a curdling chemical, transglutaminase orthe like is added to the protein-containing solution, and is thenheated.

FIG. 1 is a flowchart showing a first conventional method ofmanufacturing a protein gel, and FIG. 2 is a temperature profile in thefirst conventional method of manufacturing a protein gel. In FIG. 2, theabscissa represents time while the ordinate represents temperature.

As shown in FIGS. 1 and 2, in the first step, the temperature of aprotein-containing solution is elevated from about 80° C. to atemperature of 130-140° C. at a time t1 to heat the solution for a fewto 10 seconds for sterilization.

When the protein gel to be obtained is tofu, soymilk is used as theprotein-containing solution. A process for manufacturing the soymilk isas follows. Soy beans are first washed and then immersed in anunillustrated immersion tank. Thereafter, the soy beans are crushed withan unillustrated grinder to obtain "go", a paste of crushed soy beans,which is then heated at a temperature of 98-105° C. for 2-5 minutes.Thereafter, tofu refuse is removed from the "go" to obtain soymilk.

In the second step, a curdling chemical is added to theprotein-containing solution at a time t2. In this step,gluconodeltalactone (GDL), magnesium chloride (MgCl₂) or the like isused as the curdling chemical. The curdling chemical is added to theprotein-containing solution after being passed through abacteria-removing filter. The temperature of the protein-containingsolution is maintained at 10° C. to prevent the chemical reaction fromproceeding, which would otherwise occur at higher temperatures.

In the subsequent third step, the protein-containing solution is mixedwith the curdling chemical at a time t3 to obtain a mixture. In thisstep, the temperature of the protein-containing solution is alsomaintained at 10° C. to prevent the chemical reaction from proceeding,which would otherwise occur at higher temperatures.

In the fourth step, the mixture is aseptically filled in anunillustrated food container at a time t4. In this step, the temperatureof the protein-containing solution is maintained at 10° C. to preventthe chemical reaction from proceeding, which would otherwise occur athigher temperatures.

In the fifth step, the mixture is heated at a temperature of 90-95° C.for 30 minutes, at a time t5, for curdling the protein-containingsolution in the mixture by the action of the curdling chemical.

A protein gel can be manufactured in this manner.

FIG. 3 is a flowchart showing a second conventional method ofmanufacturing a protein gel, and FIG. 4 is a temperature profile in thesecond conventional method of manufacturing a protein gel. In FIG. 4,the abscissa represents time while the ordinate represents temperature.

As shown in FIGS. 3 and 4, in the first step, a protein-containingsolution is cooled from about 80° C. to a temperature of 25-50° C. at atime t11. To a cooled solution, transglutaminase is added.Transglutaminase is an enzyme serving as a catalyst in an acyltransferring reaction of a Υ-carboxyamide group, which is a glutamineresidue in a peptide chain.

In the second step, the protein-containing solution is mixed withtransglutaminase at a time t12. In this step, the temperature of theprotein-containing solution is maintained at 25-50° C. to prevent thecatalytic reaction from proceeding by the presence of transglutaminase,which would otherwise occur at higher temperatures.

In the subsequent third step, the mixture of the protein-containingsolution and transglutaminase is filled in an unillustrated foodcontainer at a time t13. In this step, the temperature of the mixture isalso maintained at 10-60° C., preferably at 25-50° C., to prevent thecatalytic reaction from proceeding by the presence of transglutaminase,which would otherwise occur at higher temperatures.

In the fourth step, the mixture is heated at a low-temperature of 40°C., at a time t14, so as to accelerate the catalytic reaction bytransglutaminase, thereby obtaining a protein gel.

In the fifth step, the protein gel is heated at a high-temperature of90° C., at a time t15, to inactivate transglutaminase.

A protein gel can be manufactured in this manner.

However, in the above-described conventional method of manufacturing aprotein gel in which a curdling chemical is used, a mixture of aprotein-containing solution and a curdling chemical must be heated at atemperature of 90-95° C. for 30 minutes in the fifth step to curdle theprotein-containing solution in the mixture. In another conventionalmethod of manufacturing a protein gel in which transglutaminase is used,a mixture must be first heated at a low temperature of 40° C. in thefourth step to accelerate the catalytic reaction by transglutaminase,and then heated at a high temperature of 90° C. in the fifth step toinactivate the transglutaminase. These conventional methods, therefore,have the drawback that considerable energy is consumed in themanufacturing process, resulting in high manufacturing costs.

An object of the present invention is to solve the problems of theabove-described conventional methods of manufacturing a protein gel andto provide a method of manufacturing a protein gel which can reduce themanufacturing costs.

DISCLOSURE OF THE INVENTION

To achieve the object, a method of manufacturing a protein gel accordingto the present invention includes a first step of heating aprotein-containing solution for sterilization, a second step of coolingthe protein-containing solution and adding an enzyme thereto, a thirdstep of mixing the protein-containing solution and the enzyme to obtaina mixture, a fourth step of aseptically filling the mixture in a foodcontainer, and a fifth step of allowing the aseptically filled mixtureto stand at ambient temperature.

The enzyme denatures protein in the protein-containing solution whilethe mixture is allowed to stand at ambient temperature in the fifthstep.

Since the mixture is not required to be heated for denaturing theprotein in the protein-containing solution, the energy consumed in themanufacturing process is reduced, thereby lowering the manufacturingcosts.

In another method of manufacturing a protein gel according to thepresent invention, the enzyme is transglutaminase. In this case, the useof the transglutaminase stabilizes the denaturation of protein in theprotein-containing solution.

In still another method of manufacturing a protein gel according to thepresent invention, the amount of the transglutaminase added to theprotein-containing solution is determined corresponding to the degree ofdenaturation of the protein in the protein-containing solution.Accordingly, the amount of transglutaminase can be reduced to thesmallest amount which is necessary for the denaturation of protein inthe protein-containing solution, thereby lowering the manufacturingcosts.

Still another method of manufacturing a protein gel according to thepresent invention includes a first step of heating a protein-containingsolution for sterilization, a second step of cooling theprotein-containing solution and adding transglutaminase, magnesiumchloride, and calcium lactate thereto, a third step of mixing theprotein-containing solution, transglutaminase, magnesium chloride, andcalcium lactate to obtain a mixture, a fourth step of asepticallyfilling the mixture in a food container, and a fifth step of allowingthe aseptically filled mixture to stand at ambient temperature.

The transglutaminase, magnesium chloride, and calcium lactate denatureprotein in the protein-containing solution while the mixture is allowedto stand at ambient temperature in the fifth step.

Since the mixture is not required to be heated for denaturing theprotein in the protein-containing solution, the energy consumed in themanufacturing process is reduced, thereby lowering the manufacturingcosts.

Also, since the amount of transglutaminase can be reduced by an amountcorresponding to the amounts of magnesium chloride and calcium lactateadded to the protein-containing solution, the manufacturing costs can befurther reduced.

In still another method of manufacturing a protein gel according to thepresent invention, transglutaminase is added to the protein-containingsolution in an amount of 10-40 units with respect to 1 g of protein.Magnesium chloride is preferably added to the solution in apredetermined amount equal to or less than 4.8% by weight with respectto the protein. Calcium lactate is preferably added to the solution in apredetermined amount equal to or less than 1.6% by weight with respectto the protein.

In this case, since the amount of transglutaminase added to theprotein-containing solution can be reduced by an amount corresponding tothe amounts of magnesium chloride and calcium lactate, the manufacturingcosts can be lowered. In addition, since the bitterness of the proteingel caused by magnesium chloride is suppressed, taste of the protein gelcan be prevented from being poor. Moreover, since the water-solubilityof calcium lactate can be retained, calcium lactate is prevented frombeing present in the protein gel as a solid matter.

In still another method of manufacturing a protein gel according to thepresent invention, the temperature of the protein-containing solution inthe third step and the temperature of the mixture in the fourth step aremaintained at 10-60° C. In this case, the catalytic reaction can beprevented from proceeding in the third and fourth steps.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a flowchart showing a first conventional method ofmanufacturing a protein gel;

FIG. 2 is a temperature profile in the first conventional method ofmanufacturing a protein gel;

FIG. 3 is a flowchart showing a second conventional method ofmanufacturing a protein gel;

FIG. 4 is a temperature profile in the second conventional method ofmanufacturing a protein gel;

FIG. 5 is a flowchart showing a method of manufacturing a protein gelaccording to an embodiment of the present invention;

FIG. 6 is a temperature profile in the method of manufacturing a proteingel according to the embodiment of the present invention;

FIG. 7 is a chart showing a gel property of the protein gel according tothe embodiment of the present invention;

FIG. 8 is a chart showing the strength and gel property of the proteingel; and

FIG. 9 is a flowchart showing an example of a process for manufacturinga protein gel according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will now be described in detailwith reference to the drawings.

FIG. 5 is a flowchart showing a method of manufacturing a protein gelaccording to an embodiment of the present invention, and FIG. 6 is atemperature profile in the method of manufacturing a protein gelaccording to the embodiment of the present invention. In FIG. 6, theabscissa represents time while the ordinate represents temperature.

As shown in FIG. 5, in the first step, the temperature of aprotein-containing solution is elevated from about 80° C. to 140° C., ata time t21, to heat the protein-containing solution for a few to 10seconds for sterilization. The protein-containing solution encompassesslurries, emulsions, paste-like fluids, and the like.

When the protein gel to be obtained is tofu, soymilk is used as theprotein-containing solution. First, a process for manufacturing thesoymilk will be described. Soy beans are washed and then immersed in anunillustrated immersion tank. Thereafter, the soy beans are crushed withan unillustrated grinder to obtain "go", a paste of crushed soy beans,which is then heated at a temperature of 98-105° C. for 2-5 minutes todenature the protein. Thereafter, tofu refuse is removed from the "go"to obtain soymilk. The denaturation of protein means the phenomenon inwhich hydrogen bonds, ionic bonds, or part of --S--S bonds in proteinare cut so that the regularly aligned protein structure is turned to bea network structure.

In the second step, the protein-containing solution is cooled to atemperature of 10-60° C., preferably of 25-50° C. at a time t22, andthen transglutaminase is added to the solution. Transglutaminase is anenzyme serving as a catalyst in an acyl transferring reaction ofτ-carboxyamide group, which is a glutamine residue in a peptide chain.Transglutaminase can consistently denature the protein in theprotein-containing solution.

In addition to the transglutaminase, other curdling chemicals may beadded to the protein-containing solution in an amount of 0.2-0.5% byweight. Examples of such curdling chemicals include acids such asgluconodelta lactone, and divalent cations such as magnesium chloride,calcium sulfate, magnesium sulfate, calcium chloride, etc.

As a result, the amount of transglutaminase can be reduced to lower themanufacturing costs. The amount of transglutaminase can be reduced tothe smallest amount which is necessary to curdle protein in theprotein-containing solution. The curdling of protein is the phenomenonin which the higher-order structure of denatured protein changes. Whenthe protein in the protein-containing solution denatures, it becomeseasier for the above-mentioned divalent cations to enter the proteinstructure, so that the protein-containing solution starts to curdle.

In the subsequent third step, the protein-containing solution is mixedwith the transglutaminase at a time t23 to obtain a mixture. In thisstep, the temperature of the protein-containing solution is maintainedat 10-60° C., preferably at 25-50° C., to prevent the catalytic reactionfrom proceeding, which would otherwise occur at higher temperatures.

In the fourth step, the mixture is aseptically filled in anunillustrated food container at a time t24. In this step, thetemperature of the protein-containing solution is also maintained at10-60° C., preferably at 25-50° C., to prevent the catalytic reactionfrom proceeding by transglutaminase, which would otherwise occur athigher temperatures.

In the fifth step, at a time t25, the mixture which has been asepticallyfilled in the food container is allowed to stand at ambient temperature(for example, 25° C.) for about 1-7 days. The transglutaminase graduallycurdles and ripens the protein in the protein-containing solution.

A-protein gel can be manufactured in this way.

In the case where transglutaminase is added to the soymilk tomanufacture tofu, 2,000 units (1 activa-TG/source material powder=10,000units/g) of transglutaminase are needed for 1 g of protein. This resultsin increased costs.

By adding a predetermined amount of magnesium chloride, and apredetermined amount of calcium lactate in the soymilk, the amount oftransglutaminase added to the soymilk can be reduced. If magnesium isadded to the soymilk in an amount greater than 6.0% by weight, a strangetaste is caused, thereby deteriorating the taste of tofu. If calciumlactate is added to the soymilk in an amount greater than 2.0% byweight, the calcium lactate saturates, so that part of the calciumlactate remains as a solid matter and is caught by the bacteria-removingfilter. Also, it gives a granular texture to tofu.

In the present embodiment, 10-40 units of transglutaminase with respectto 1 g of protein, a predetermined amount of 4.8% or less of magnesiumchloride (by weight with respect to the total weight of protein), and apredetermined amount of 1.6% or less of calcium lactate (by weight withrespect to the total weight of protein) were added to and mixed with thesoymilk which was maintained at 10-60° C., preferably at 25-50° C.Thereafter, the mixture of soymilk, transglutaminase, magnesiumchloride, and calcium lactate was aseptically filled in a food containerand was allowed to stand at 25° C. for 2-5 days. As a result, tofu whichwas free of strange taste and granular texture was obtained.

Also, in the case where the transglutaminase, magnesium chloride, andcalcium lactate were added to and mixed with soymilk, which wasmaintained at 10-60° C., preferably at 25-40° C., so as to obtain amixture, and the mixture was then aseptically filled in a food containerand was allowed to stand at 25° C. for 2-5 days, fine textured tofu wasobtained, which was free of strange taste and granular texture, and inwhich separation of water was reduced.

In the case where the transglutaminase, magnesium chloride, and calciumlactate were added to and mixed with soymilk maintained at 20° C. so asto obtain a mixture, and the mixture was then aseptically filled in afood container and was allowed to stand at 10° C. or lower for 2-5 days,the soymilk did not curdle.

Next, the properties of a protein gel manufactured by the method ofmanufacturing a protein gel according to the embodiment of the presentinvention will be described.

FIG. 7 is a chart showing a gel property of a protein gel according tothe embodiment of the present invention, FIG. 8 is a chart showing thestrength and gel property of the protein gel, and FIG. 9 is a flowchartshowing an example of a process for manufacturing a protein gelaccording to the present invention. In FIG. 7, the abscissa representsthe amount of penetration of a plunger while the ordinate represents thepressure acting on the plunger. In FIG. 8, the abscissa representspressure at which breakage of gel occurred (hereinafter referred to as"gel breakage strengths") while the ordinate represents the amount ofpenetration of the plunger.

Tofu 11 was manufactured by the procedure shown in FIG. 9 and itsproperties were examined. In the manufacture of the tofu 11, 10 units oftransglutaminase with respect to 1 g of protein, 4.8% by weight ofmagnesium chloride, and 1.6%. by weight of calcium lactate were added tosoymilk.

As shown in FIG. 7, a plunger 12 having a diameter of 10 mm was disposedperpendicularly to the surface of the tofu 11 and was advanced in thedirection indicated by arrow A toward the tofu 11 at a speed of 10cm/min. The relationship between the pressure applied to the plunger 12and the amount of penetration of the plunger was examined, using thesurface of the tofu as a zero position (0 mm) for the amount ofpenetration of the plunger.

When the pressure applied to the plunger 12 increased, the tip of theplunger 12 broke the surface of the tofu 11 at a gel breakage point Band entered inside the tofu 11.

When the relationship between the gel breakage strength at the gelbreakage point B and the amount of penetration of the plunger wasexamined for a plurality of pieces of tofu 11 and was plotted, theplotted dots were located within an area Ar1 of FIG. 8. From this, itwas revealed that the tofu 11 had a sufficiently high gel breakagestrength, and the amount of penetration of the plunger was sufficientlylarge, compared to conventional tofu.

The area Ar2 of FIG. 8 shows a range in which each dots representing therelationship between the gel breakage strength and the amount ofpenetration of the plunger were located when the above-described testwas performed using tofu 11 manufactured by a conventional method.

The unillustrated food container may be a brick-shaped packagingcontainer. In this case, a web-like packaging material made of aflexible laminated material is sealed in the longitudinal direction toobtain a tubular package in an unillustrated packaging containermanufacturing apparatus. The above-described mixture is then asepticallyfilled in the tubular package, which is sealed in the lateral directionto obtain packaging containers. For example, the packaging material maybe the type in which polyethylene film is formed on both sides of apaper substrate as innermost and outermost layers.

When such a packaging container is used as a food container in theconventional method of manufacturing a protein gel, a problem occursbecause a mixture must be heated after being filled in the foodcontainer. That is, since the polyethylene layer is softened duringheating, the sealed portions or the flap portions (triangular tabportions) of the container separates, or the protein gel is set on thepolyethylene layer. Also, air or the like dissolved in the mixtureexpands, so that the food container is deformed. In the case where thefood container is immersed in hot water to heat the mixture, waterpenetrates into the substrate, thereby decreasing the strength of thefood container.

By contrast, in the method of manufacturing a protein gel according tothe present invention, the mixture is not required to be heated afterbeing filled in the food container. Accordingly, the sealing portionsand flap portions of the food container are prevented from separating,and the protein gel is prevented from setting on the polyethylene layer.Also, the food container is not deformed due to expansion of air or thelike dissolved in the mixture. In addition, the strength of the foodcontainer is prevented from decreasing due to soaking of water into thesubstrate of the packaging material.

The present invention is not limited to the above-described embodiments,and various modifications and variations can be made based on the spiritof the present invention. Therefore, these modifications and variationsshould not be construed to be excluded from the scope of the presentinvention.

INDUSTRIAL APPLICATION

The present invention can be applied to apparatuses for manufacturing aprotein gel such as tofu to be filled in a food container.

I claim:
 1. A method of manufacturing a tofu protein gel comprising:(a)heating a soy protein-containing solution for sterilization; (b) coolingsaid sterilized soy protein-containing solution to a temperature withina range sufficiently low to prevent curdling of the soy protein uponaddition of transglutaminase thereto; (c) mixing said sterilized soyprotein-containing solution and the transglutaminase to obtain a mixturewhile maintaining the temperature of said sterilized protein-containingsolution within said range; (d) aseptically filling said mixture in afood container while maintaining the temperature of said sterilizedprotein-containing solution within said range; and (e) reacting thetransglutaminase with the soy protein-containing solution at ambienttemperature to curdle the soy protein and form the tofu by allowing saidaseptically filled mixture to stand in said container at ambienttemperature.
 2. A method of manufacturing a tofu protein gel accordingto claim 1, wherein the amount of said transglutaminase added to saidprotein-containing solution is 10-40 units per 1 g of said soy protein.3. A method of manufacturing a tofu protein gel comprising:(a) heating asoy protein-containing solution for sterilization; (b) cooling said soyprotein-containing solution to a temperature within a range sufficientlylow to prevent curdling of the soy protein upon addition oftransglutaminase, magnesium chloride, and calcium lactate thereto; (c)mixing said soy protein-containing solution, transglutaminase, magnesiumchloride, and calcium lactate to obtain a mixture while maintaining thetemperature of said sterilized soy protein-containing solution withinsaid range; (d) aseptically filling said mixture in a food containerwhile maintaining the temperature of said sterilized soyprotein-containing solution within said range; and (e) reacting thetransglutaminase, magnesium chloride and calcium lactate with the soyprotein-containing solution at ambient temperature to curdle the soyprotein and form the tofu by allowing said aseptically filled mixture tostand in said container at ambient temperature.
 4. A method ofmanufacturing a protein gel according to claim 3, wherein saidtransglutaminase is added to said protein-containing solution in anamount of 10-40 units with respect to 1 g of protein, said magnesiumchloride is added to said solution in a predetermined amount equal to orless than 4.8% by weight with respect to the protein, and said calciumlactate is added to said solution in a predetermined amount equal to orless than 1.6% by weight with respect to the protein.
 5. A method ofmanufacturing a protein gel according to claim 1, wherein thetemperature of said soy protein-containing solution in the third stepand the temperature of said mixture in the fourth step are maintained at10-60° C.
 6. A method according to claim 1 wherein said range is 10-60°C.
 7. A method according to claim 1 wherein said range is 25-50° C.
 8. Amethod according to claim 6 wherein said the heating for sterilizationis at a temperature of 80-140° C. for no longer than 10 seconds.
 9. Amethod according to claim 1 wherein said heating for sterilization is at80-140° C. for no longer than 10 seconds.
 10. A method according toclaim 2 wherein said range is 10-60° C.
 11. A method according to claim2 wherein said range is 25-50° C.
 12. A method according to claim 10wherein said the heating for sterilization is at a temperature of80-140° C. for no longer than 10 seconds.
 13. A method according toclaim 11 wherein said the heating for sterilization is at a temperatureof 80-140° C. for no longer than 10 seconds.